Image processing apparatus, ultrasonic imaging apparatus, and imaging processing method for improving image quality based on conversion relating to virtual illumination position

ABSTRACT

Disclosed herein is an image processing apparatus. The image processing apparatus collects volume data which relates to an object, generates volume-rendered image data from the collected volume data, acquires a projection image of the object at a position at which virtual illumination is emitted toward the object, based on the volume-rendered image data, and corrects the projection image by using at least one conversion function, thereby obtaining a result image.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from Korean Patent Application No.10-2013-0007494, filed on Jan. 23, 2013 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND 1. Field

Exemplary embodiments relate to an image processing apparatus andmethod.

2. Description of the Related Art

In modern times, a variety of imaging apparatuses have been used inorder to capture images of the exteriors or interiors of objects.

Examples of various imaging apparatuses include a camera, a digitalradiography (DR) apparatus, a computed tomography (CT) apparatus, amagnetic resonance imaging (MRI) apparatus, and an ultrasonic imagingapparatus.

These imaging apparatuses collect various data which relate to an objectby using visible light, infrared light, radiation such as X-rays, and/orultrasonic waves, and generate an image by using the collected data.

A user can neither directly interpret nor read data which is collectedby such imaging apparatuses, and thus, a process for converting thecollected data via a predetermined image processing unit of the imagingapparatuses into an image that can be viewed by a user is generallyperformed via predetermined image processing.

SUMMARY

Therefore, it is an aspect of one or more exemplary embodiments toprovide an image processing apparatus and method that may improve aquality of an image which has been acquired based on collected imagedata by using at least one conversion function that varies based on achange in the position of virtual illumination, and an ultrasonicimaging apparatus to which the image processing apparatus and method areapplied.

Additional aspects of the exemplary embodiments will be set forth inpart in the description which follows and, in part, will be apparentfrom the description, or may be learned by practice of the exemplaryembodiments.

To achieve the technical goals, an image processing method, an imageprocessing apparatus, and an ultrasonic imaging are provided.

In accordance with one aspect of one or more exemplary embodiments, animage processing method includes acquiring, by an image processingapparatus, volume-rendered image data by using volume data which relateto an object and correcting the acquired image data by using at leastone conversion function which is determined based on a virtualillumination position which relates to the object. In this regard, thevirtual illumination position indicates a position at which a virtualillumination unit emits virtual illumination toward the object.

The correcting may include adjusting a brightness of the acquired imagedata by using a first conversion function which is determined based oncoordinates of the virtual illumination position, performing a tonemapping by using a second conversion function, and/or performing a huecorrection by using a third conversion function.

The first conversion function may include a function which isexpressible by Equation 1 below:

$\begin{matrix}{{l\left( {\phi,\theta} \right)} = {1 - {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

wherein (φ,θ) denotes respective coordinates of the virtual illuminationposition in a spherical coordinate system, (φ₀,θ₀) denotes respectivecoordinates of a reference position in the spherical coordinate system,σ_(φ) and σ_(θ) denote respective values which relate to a distributionof a first virtual illumination position, and A denotes a predeterminedconstant.

The second conversion function may include a function which isexpressible by Equation 2 below:

$\begin{matrix}{{p\left( {x,\phi,\theta} \right)} = \frac{1}{1 + {\alpha \cdot e^{{- {\beta{({\phi,\theta})}}} \cdot x}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

wherein x denotes an image value of a respective voxel, φ and θ denoterespective coordinates of the virtual illumination position in aspherical coordinate system, α denotes a predetermined constant, andβ(φ,θ) denotes a value which is determined based on the virtualillumination position. In this case, β(φ,θ) may be determined byapplying Equation 3 below.

$\begin{matrix}{{\beta\left( {\phi,\theta} \right)} = {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

wherein (φ₀,θ₀) denotes respective coordinates of a reference positionin the spherical coordinate system, σ_(φ) and σ_(θ) denote respectivevalues which relate to a distribution of a first virtual illuminationposition, and A denotes a predetermined constant.

The third conversion function may include a function which isexpressible by Equation 4 below:C(x,s,φ,θ)=x·s·[(1−ϵ)+ϵ·l(φ,θ)]  [Equation 4]

wherein x denotes an image value of a respective voxel, s denotes ashadow value, φ and θ denote respective coordinates of the virtualillumination position in a spherical coordinate system, ϵ denotes aluminance attenuation constant, and l(φ,θ) denotes a luminanceattenuation value which relates to the virtual illumination position.

In accordance with another aspect of one or more exemplary embodiments,an image processing apparatus includes a volume data collector which isconfigured to collect volume data which relate to an object and an imageprocessor which is configured to acquire rendered image data byperforming volume rendering with respect to the collected volume dataand to correct the collected image data by using at least one conversionfunction which is determined based on a virtual illumination positionwhich relates to the object. In this regard, the at least one conversionfunction may include at least one of the first, second and thirdconversion functions.

In accordance with another aspect of one or more exemplary embodiments,an ultrasonic imaging apparatus includes an ultrasonic probe which isconfigured to transmit ultrasonic waves to an object and to receiveultrasonic echo waves which are reflected from the object, a beamformerwhich is configured to perform beamforming based on the ultrasonic echowaves which are received by the ultrasonic probe, a volume datagenerator which is configured to acquire volume data which relate to theobject based on the resulting beamformed data, and an image processorwhich is configured to acquire image data by performing volume renderingwith respect to the volume data and to correct the acquired image databy using at least one conversion function which is determined based on avirtual illumination position which relates to the object. In thisregard, the at least one conversion function may include at least one ofthe first, second and third conversion functions.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee. The foregoing and/or other aspects will becomeapparent and more readily appreciated from the following description ofthe exemplary embodiments, taken in conjunction with the accompanyingdrawings of which:

FIG. 1 is a block diagram which illustrates a configuration of an imageprocessing apparatus, according to an exemplary embodiment;

FIG. 2 is a block diagram of an image processor of the image processingapparatus, according to an exemplary embodiment;

FIG. 3 is a view which illustrates an emission of virtual illuminationtoward an object;

FIGS. 4A and 4B illustrate images which are respectively acquired byemitting virtual illumination toward rear and front surfaces of theobject;

FIG. 5 is a view which illustrates a method for performing a conversionbetween a rectangular coordinate system and a spherical coordinatesystem;

FIG. 6 is a graph which illustrates a β function, according to anexemplary embodiment;

FIG. 7 is a graph which illustrates a first conversion function,according to an exemplary embodiment;

FIG. 8 is a view which illustrates a conversion of θ values;

FIG. 9 is a graph which illustrates forms of a second conversionfunction which vary based on a change in the β value;

FIGS. 10A and 10B illustrate corrected images, according to an exemplaryembodiment;

FIG. 11 is a perspective view of an ultrasonic imaging apparatus,according to an exemplary embodiment;

FIG. 12 is a block diagram which illustrates a configuration of theultrasonic imaging apparatus, according to an exemplary embodiment;

FIG. 13 is a flowchart which illustrates an image processing method,according to an exemplary embodiment;

FIG. 14 is a flowchart which illustrates an image processing method,according to another exemplary embodiment; and

FIG. 15 is a flowchart which illustrates a process for correcting animage based on a virtual illumination position.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout.

FIG. 1 is a block diagram which illustrates a configuration of an imageprocessing apparatus M, according to an exemplary embodiment.

As illustrated in FIG. 1, the image processing apparatus M includes animage data collector 10 which is configured to collect image data whichis used to generate an image of an object ob and an image processor 100which is configured to generate a result image by performingpredetermined image processing on the image data collected by the imagedata collector 10.

The image data collector 10 collects raw image data from the object ob.In this regard, the raw image data may include volume data that providesa three-dimensional representation of the object ob.

The image data collector 10 may include, for example, an ultrasonicprobe that transmits ultrasonic waves to the object ob and receives anultrasonic echo signal which is reflected from the object ob in animaging apparatus m according to an exemplary embodiment, i.e., anultrasonic imaging apparatus. In a case in which the image processingapparatus m is applied to a CT apparatus, the image data collector 10may include a radiation emission module which is configured to irradiatean object with radiation such as X-rays, a radiation detection modulewhich is configured to detect radiation which has propagated through theobject or radiation which directly reaches the radiation detectionmodule without having passed through the object, and the like. When amagnetic resonance imaging apparatus is used as the image processingapparatus m, the image data collector 10 may include a high frequencycoil which is configured to apply electromagnetic waves to an objectwhich is exposed to a static magnetic field and a gradient magneticfield and to receive a magnetic resonance signal which is generated dueto a magnetic resonance phenomenon of atomic nuclei inside the object inresponse to the applied electromagnetic waves, and the related devices.

The image processor 100 performs rendering based on image data whichrelate to the object and are collected by the image data collector 10,corrects the rendered image data in order to generate a final image, andtransmits the corrected image data to an output unit 102 which isinstalled in an external workstation which is connected to the imageprocessing apparatus M via a wired or wireless communication network orinstalled in the image processing apparatus M, the output unit 102including, e.g., a device which includes a display unit such as a smartphone, a monitor, or the like, or an image forming apparatus such as aprinter so that a user can check the resultant corrected image.

In this case, the image processor 100 may be connected to the imageprocessing apparatus M via a wired or wireless communication network, orreceive predetermined commands or instructions from a user via an inputunit 101 which is installed in the image processing apparatus M. Theimage processor 100 may be configured to initiate rendering or imagecorrection based on the predetermined commands or instructions which areinput via the input unit 101, or to generate or revise various settingswhich may be needed for rendering or image correction and then performrendering or image correction based on the generated or revisedsettings. In this regard, the input unit 101 may include any one or moreof various members that enable a user to input data, instructions, orcommands, such as, e.g., a keyboard, a mouse, a trackball, a tablet, atouch screen, and/or the like.

When the image data includes volume data which relates to the object ob,the image processor 100 may acquire a projection image of the object obwhich corresponds to one or more view points of a user. In addition, theimage processor 100 corrects the image data collected by the image datacollector 10 based on a position of virtual illumination which isemitted toward the object ob and rendered in order to acquire a resultimage. In this case, the view points of a user and/or the position ofvirtual illumination may be input via the input unit 101.

FIG. 2 is a block diagram which illustrates the imaging processor 100,according to an exemplary embodiment.

As illustrated in FIG. 2, the imaging processor 100 may include arendering unit 110 (also referred to herein as a renderer 110), aprojection image acquisition unit 120 (also referred to herein as aprojection image acquirer 120), a virtual illumination processor 130,and an image correction unit 140 (also referred to herein as an imagecorrector 140).

The rendering unit 110 performs rendering based on image data which iscollected and which relate to the object ob. In particular, thecollected image data are mixed to reconstruct a 2D or 3D image of theobject ob. When the image data collected by the image data collector 10are volume data which are represented by a plurality of voxels, therendering unit 110 performs volume rendering upon the collected volumedata of the object ob in order to reconstruct image data into a 3Dvisual image. Accordingly, a 3D image of the object ob is acquired.

According to one or more exemplary embodiments, the rendering unit 110may perform rendering by using information which relates to apredetermined position of virtual illumination which is emitted towardthe object ob, i.e., a shadow map which is generated based on thepredetermined position of the virtual illumination. In this regard, theposition of the virtual illumination indicates information which relatesto a position at which illumination is to be virtually emitted towardthe object ob as illustrated in FIG. 3. In addition, a shadow map is aresult of mapping a resultant texture of the rendered shadows, whichreflect a shape of the object ob, to an image of the object ob, whenillumination is emitted toward the object in the image from a particularposition.

According to one exemplary embodiment, the rendering unit 110 maygenerate the above-described shadow map based on the predeterminedposition of the virtual illumination and then perform rendering by usingthe generated shadow map.

In this case, the rendering unit 110 may perform rendering by receivingthe position of the virtual illumination from the virtual illuminationprocessor 130 of FIG. 2, generating a shadow map based on the receivedposition of the virtual illumination, and adding the generated shadowmap to volume data. In addition, the rendering unit 110 may read out theposition of virtual illumination which is stored in a separate storagespace connected to the rendering unit 110, e.g., a volatile memory or anon-volatile memory, generate a shadow map based thereon, and performrendering by using the shadow map, in order to generate a shaded 3Dimage. In this case, the position of virtual illumination that isreceived or read out by the rendering unit 110 may be expressed ordenoted as coordinates (θ, φ) which are represented in a sphericalcoordinate system as described below.

In order to generate a shadow map, the rendering unit 110 may include ashadow processor 111 as illustrated in FIG. 2. The shadow processor 111generates a shadow map which is used for rendering of image datacollected from the object ob, in particular, volume data, so that therendering unit 110 performs volume rendering by using the generatedshadow map.

For example, the shadow processor 111 may determine a direction of ashadow to be added to the object ob based on the position of virtualillumination which is transmitted by a virtual illumination controller131 of the virtual illumination processor 130, determine a shape of theshadow to be added, based on the position of virtual illumination andthe shape of the object ob, and generate a shadow map to be used inrendering based on the determination results.

After the shadow processor 111 generates the shadow map, the renderingunit 110 reconstructs an image of the object ob to which a predeterminedshadow is added, e.g., a 3D image, by applying the generated shadow mapto the rendering of the image data. Because the shadow is represented onthe generated 3D image, the image of the object ob may be morerealistically displayed.

In another exemplary embodiment, the rendering unit 110 may receive ashadow map from a separate storage device or the virtual illuminationprocessor 130 without directly generating a shadow map and then use thereceived shadow map in a rendering process.

In addition, the rendering unit 110 may perform rendering of volume databy using any one or more of various other methods in addition to shadowmapping so that a shadow is formed on the rendered image.

As illustrated in FIG. 2, the image processor 100 may include theprojection image acquisition unit 120 which is configured to generate aprojection image which corresponds to a predetermined view point basedon the image data rendered by the rendering unit 110 or a result imagewhich has been corrected by the image correction unit 140, which will bedescribed below.

When image data which relate to the object ob are volume data whichrelate to the object ob which data include 3D information, theprojection image acquisition unit 120 acquires a 2D image (i.e.,projection image) which corresponds at least one view point, i.e., atleast one angle, based on a 3D image of the object ob which is obtainedvia volume rendering which is performed by the rendering unit 110, orbased on a 3D image which has undergone volume rendering and beencorrected by the image correction unit 140. In this regard, the viewpoint of the object ob may be predetermined based on a setting that ispreset in the image processing apparatus M, or may be input by a uservia any one or more of various kinds of input units (i.e., an input unit101) which are installed in the image processing apparatus M orconnected thereto via a wired or wireless communication network, such asa keyboard, a mouse, a touch screen, a trackball, and/or the like.

The virtual illumination processor 130 of the image processor 100transmits various data for the virtual illumination, e.g., positioninformation which relates to the virtual illumination, to the renderingunit 110 or the image correction unit 140, so that the rendering unit110 or the image correction unit 140 reconstructs a 3D image to which ashadow which relates to the virtual illumination is applied and/orcorrects luminance and/or contrast of the acquired 3D image.

FIG. 3 is a view which illustrates an emission of virtual illuminationtoward an object ob. FIGS. 4A and 4B illustrate images acquired byemitting virtual illumination toward rear and front surfaces of theobject ob.

As illustrated in FIG. 3, when an illumination unit irradiates theobject ob with light from a predetermined position, e.g., a firstposition a1, a shadow s1 of the object ob is generated in a directionwhich is opposite to a direction of the illumination unit (i.e., anX-axis direction) with respect to the object ob. In this case, when aview point b1 is located in the direction which is opposite to directionof the illumination unit with respect to the object ob, the object obappears dark due to the shadow s1 from the view point. By contrast, in acase in which the illumination unit irradiates the object ob with lightfrom a second position a2, when the view point b1 is located in the samedirection or approximately the same direction as that of theillumination unit or at a position which is relatively nearby to that ofthe illumination unit, the object ob appears brighter due to increasedluminance.

A virtual illumination unit virtually emits light toward the object ob,similarly as would be emitted by an actual illumination unit. Thus, evenwhen virtual illumination is emitted, image processing is needed inorder to display a shadow, rim light, or the like similarly to a case inwhich actual illumination is emitted.

In particular, as illustrated in FIG. 4A, when virtual illumination isemitted from a rear direction v₁ (see also FIG. 5) with respect to theobject ob, i.e., when the virtual illumination includes backlight, anedge of the object ob distinctly appears relatively bright due tobacklight derived from the virtual illumination, and a central region ofthe object ob appears relatively darker.

By contrast, as illustrated in FIG. 4B, when virtual illumination isemitted from a front surface of the object ob, i.e., when virtualillumination includes front light, a central region of the object obappears relatively bright, whereas a contrast quality of the acquiredimage or 3D properties thereof may be reduced due to increased luminanceand light scattering.

The virtual illumination processor 130 stores and/or processes varioustypes of information which relate to the virtual illumination, e.g.,information which relates to a predetermined emission direction ordistance of the virtual illumination, i.e., a position of the virtualillumination unit, the amount of the virtual illumination, and the like,and transmits the various information which relates to the virtualillumination to the rendering unit 110 and/or to the image correctionunit 140. In accordance with the transmitted information which relatesto the virtual illumination, the rendering unit 110 and/or the imagecorrection unit 140 may generate a shadow or the like in a 3D image ofthe object ob, and/or correct the size or concentration of shadow,brightness of the object ob, or the like.

As illustrated in FIG. 2, the virtual illumination processor 130 mayinclude the virtual illumination controller 131, a coordinate converter132, and a storage unit 133.

The virtual illumination controller 131 transmits various informationwhich relates to the virtual illumination and/or control commands whichrelate to the virtual illumination to the rendering unit 110 or eachelement of the virtual illumination processor 130, e.g., the coordinateconverter 132 and the storage unit 133. As desired, the virtualillumination controller 131 may receive position information whichrelates to the virtual illumination and/or information which relates tothe amount or the like of the virtual illumination from a user via theinput unit 101, and then transmit the received information to eachelement of the virtual illumination processor 130 or generate separatecontrol commands based on the received information and transmit thecontrol commands to each element of the virtual illumination processor130. In addition, the virtual illumination controller 131 may read outvarious predetermined setting information and/or data which relate tothe virtual illumination from a separate storage space, and thentransmit the read-out information to each element thereof or generatecontrol commands based on the information.

After the position of the virtual illumination is determined by thevirtual illumination controller 132, the determined position of thevirtual illumination may be transmitted to the rendering unit 110. Then,the rendering unit 110 may further add a shadow to the 3D image of theobject ob based on the transmitted position of the virtual illumination.

As described above, if the rendering unit 100 reads out informationwhich relates to the virtual illumination from a separate storage space,the virtual illumination processor 130 may receive the information whichrelates to the virtual illumination read by the rendering unit 110. Inthis case, the virtual illumination controller 131 of the virtualillumination processor 130 determines a position of the virtualillumination based on the information which relates to the virtualillumination.

When the position of the virtual illumination is represented by using arectangular coordinate system having x, y and z axes, i.e., whenposition values of the virtual illumination are represented as (x, y,z), the coordinate converter 132 of the virtual illumination processor130 converts coordinates of the virtual illumination position in therectangular coordinate system into coordinates in a spherical coordinatesystem.

FIG. 5 is a view which illustrates a method for conversion between arectangular coordinate system and a spherical coordinate system,according to an exemplary embodiment. As illustrated in FIG. 5, it isassumed that a first virtual illumination position v₁ has coordinates(x₁, y₁, z₁) in the rectangular coordinate system, an angle between avector v₁ which corresponds to the first virtual illumination positionand the z axis is θ₁, and an angle between a vector v₁′ obtained byprojecting the vector v₁ onto an x-y plane and the x axis is φ₁. In thiscase, a distance between the first virtual illumination position and theorigin, i.e., an absolute value r of the vector v₁ for the first virtualillumination position, may be obtained by applying Equation 1 below:r=√{square root over (x ₁ ² +y ₁ ² +z ₁ ²)}  [Equation 1]

In addition, the angle θ₁ between the vector v₁ and the z axis and theangle φ₁ between the vector v₁′ and the x axis may be obtained byrespectively applying Equations 2 and 3 below:

$\begin{matrix}{\theta_{1} = {\cos^{- 1}\left( \frac{z_{1}}{r} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \\{\phi_{1} = {\tan^{- 1}\left( \frac{y_{1}}{x_{1}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

By using Equations 1, 2, and 3, the coordinates represented as (x₁, y₁,z₁) in the rectangular coordinate system may be converted into (θ₁, φ₁),which are coordinates in the spherical coordinate system. By convertingcoordinates in the rectangular coordinate system into coordinates in thespherical coordinate system, the number of variables may be decreased,thereby simplifying computation.

In some exemplary embodiments, the coordinates (θ, φ) in the sphericalcoordinate system may not be defined as illustrated in FIG. 5. Forexample, the value θ may be defined as an angle between the x-y planeand the vector v₁. Even in this case, the coordinate (θ, φ) may beobtained using the inverse of a sine function, a cosine function, or atangent function similarly as described above.

The virtual illumination position value (θ,φ) which is obtained bycalculating and converting into the coordinates in the sphericalcoordinate system by using the coordinate converter 132 may betemporarily or permanently stored in the storage unit 133. Theabove-described rendering unit 110 or the image correction unit 140,which will be described below, may read out the converted coordinatesfor the virtual illumination position and then perform rendering orimage correction accordingly.

The image correction unit 140 of the image processor 100 corrects anacquired image by performing predetermined image processing on theacquired image data, e.g., rendered volume data or a projection imagewhich corresponds to at least one view point for the rendered volumedata. The image correction unit 140 may receive the information whichrelates to the virtual illumination from the virtual illuminationprocessor 130 as in the rendering unit 110. In this case, theinformation which relates to the virtual illumination may includecoordinates in a spherical coordinate system, as described above. Inaddition, the image correction unit 140 may receive a conversionfunction which is appropriate for image correction by reading aconversion function database 150. The image correction unit 140 maycorrect volume data or a projection image which corresponds to at leastone view point based on the volume data by using the received orread-out virtual illumination position and at least one conversionfunction (e.g., correction of luminance, contrast, hue or the like ofthe projection image), thereby generating a result image.

The image correction unit 140 may include a first correction unit 141, asecond correction unit 142, and a third correction unit 143, asillustrated in FIG. 2.

The first correction unit 141 may be configured to adjust a brightnessof image data, e.g., a projection image which is acquired by theprojection image acquisition unit 120. According to one exemplaryembodiment, the first correction unit 141 may read out a firstconversion function F1 which is extracted from the conversion functiondatabase 150 and then adjust a brightness of the projection image byapplying the first conversion function F1 to the acquired projectionimage. In this case, the first conversion function F1 which is appliedto the projection image may include an illumination attenuation functionwhich is used to adjust a brightness attenuation of the projectionimage.

In particular, in one exemplary embodiment, the first conversionfunction F1 may be expressible by Equation 4 below:l(φ,θ)=1−β(φ,θ)  [Equation 4]

In this regard, β(φ,θ) (hereinafter referred to as the “β function”) isa value which is determined based on the position of virtualillumination. In one exemplary embodiment, the β function used inoperation of the first conversion function F1 may take the same form asa Gaussian function.

In particular, according to one exemplary embodiment, the β function maybe expressible by Equation 5 below:

$\begin{matrix}{{\beta\left( {\phi,\theta} \right)} = {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In this regard, (φ, θ) denotes coordinates which are calculated by thecoordinate converter 132 or the like or a pre-given coordinate pair forthe virtual illumination position in a spherical coordinate system, and(φ₀, θ₀) denotes coordinates of a reference position in the sphericalcoordinate system. For example, (φ₀, θ₀) may be (0, 0). In Equation 5,σ_(φ), and σ_(θ) denote respective values which relate to a distributionof the virtual illumination position, and A denotes a constant that ispredetermined based on a selection by a user, a manufacturer of theimage processing apparatus M, or the like. For example, A may have avalue of 1.

As represented in Equation 5, the result value of the β function, i.e.,the β value, is determined as a function of the virtual illuminationposition, e.g., the φ and θ values. The β value, i.e., the φ and θvalues, is continuously varied based on a corresponding change in thevirtual illumination position.

The β function may be illustrated as a graph as shown in FIG. 6. In FIG.6, x and y axes denote θ and φ, respectively, the z axis denotes βvalues, and the β values denote calculation results which are obtainedby substituting the φ and θ values into the β function. As illustratedin FIG. 6, the graph for the β function has a bell shape with aprotruding central portion. In this case, referring to FIG. 6, it can beconfirmed that θ and φ increase when approaching zero and have themaximum values at zero. By contrast, when any one of the θ and φ valuesis distant from zero, i.e., when approaching 2 or −2, the β valueapproximates to zero.

The β function as expressed by Equation 5 is used in the firstconversion function F1 as expressed by Equation 4, and second and thirdconversion functions F2 and F3 as expressed by Equations 8 and 9,respectively, which will be described below.

Further, the first conversion function F1 of Equation 4 may beillustrated as a graph as shown in FIG. 7. FIG. 7 is a graph of thefirst conversion function, i.e., the function l(φ,θ), which shows arelationship among θ and φ and a degree l of luminance attenuation.Equation 4 clearly illustrates that the result value of the firstconversion function F1 may be obtained by subtracting the β functionfrom the constant. Thus, as illustrated in FIG. 7, the first conversionfunction F1 may have a bell shape with a concave central portion whichis different from the β function. Accordingly, the θ and φ values of thefirst conversion function F1 decrease when approaching zero and,consequently, the values converge to zero, by contrast with the βfunction illustrated in FIG. 6. When any one of the θ and φ values isdistant from zero, i.e., when approaching 2 or −2, the first conversionfunction F1 approximates to 1. In this case, when the first conversionfunction F1 is applied to the projection image, the image appears darkas the θ and φ values approximate to zero. When both of the θ and φvalues are equal to zero, the image is darkest. Therefore, the image mayhave luminance attenuation effects based on the virtual illuminationposition.

FIG. 8 is a view which illustrates a conversion of the θ value. Whenboth of the θ and φ values are equal to zero, as illustrated in FIG. 8,a virtual illumination position is present at a point on the z axis,e.g., V₂′. Thus, in a case in which the θ and φ values are defined byEquations 1, 2, and 3, θ needs to be converted prior to substitution ofthe θ and φ values into the first conversion function F1. In this case,when the virtual illumination is on a front side of the object, i.e.,when a direction of the virtual illumination and a direction of a viewpoint are the same or approximate to each other, first, the θ value isconverted by using Equation 6 below for application to the firstconversion function F1:

$\begin{matrix}{\theta^{\prime} = {\theta - \frac{\pi}{2}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

According to Equation 6, the θ′ value is decreased by π/2 from the θvalue. FIG. 7 is a view which illustrates the first conversion functionF1. It is assumed that the coordinates (θ, φ) of a virtual illuminationposition V₂ in the spherical coordinate system prior to conversion are(0, π/2), as illustrated in FIG. 8. If the view point is positioned onthe x axis and the object ob is located at the origin O, an emissiondirection of the virtual illumination at V₂ is the same as a directionof the view point with respect to the object ob. In particular, thevirtual illumination which is emitted toward the object ob is frontlight. In this case, the θ value is converted by using Equation 6 inorder to obtain a coordinate (0, 0). More particularly, as illustratedin FIG. 8, the virtual illumination position V₂ prior to conversion istransformed into a virtual illumination position V₂′ after conversion.

The coordinate obtained by converting the θ value by using Equation 6 isapplied to the first conversion function F1. Because the coordinate (θ′,φ) to be applied to the first conversion function F1 is (0, 0), theresult value of the first conversion function F1 approximates to zero,as seen from Equations 4, 5 and 6, whereby luminance of the projectionimage may be reduced as described above.

By contrast, when the virtual illumination is located on a back side,i.e., when an emission direction of the virtual illumination isrelatively opposite to a direction of the view point with respect to theobject ob, first, the θ value is converted by using Equation 7 below tobe applied to the first conversion function F1:

$\begin{matrix}{\theta^{\prime} = {\theta + \frac{\pi}{2}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

According to one exemplary embodiment, the second correction unit 142 ofthe image correction unit 140 performs a tone mapping upon image data,e.g., the projection image acquired by the projection image acquisitionunit 120. Accordingly, contrast or the like of the image data may becorrected and/or various effects may be added to the image data.Similarly as described above, the second correction unit 142 may readout the second conversion function F2, which is a tone mapping function,which is extracted from the conversion function database 150, andperform the tone mapping by applying the read-out second conversionfunction F2 to the image data, e.g., the projection image.

In one exemplary embodiment, the second conversion function F2 may beexpressible by Equation 8 below:

$\begin{matrix}{{p\left( {x,\phi,\theta} \right)} = {\frac{1}{1 + {\alpha \cdot e^{{- {\beta{({\phi,\theta})}}} \cdot x}}}.}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In Equation 8, x denotes a respective image value (i.e., an image inputvalue) which is input to each respective pixel or voxel of an imagewhich is collected by the image data collector 10 or acquired by theprojection image acquisition unit 120. p(x,φ,θ), which is obtained as aresult of the calculation, denotes a corrected image value (i.e., animage output value) that is output as a result of calculation of theimage input value of each pixel or voxel by using Equation 8.

In addition, in Equation 8, φ and θ denote coordinates which arecalculated by the coordinate converter 132 or the like, or pre-givencoordinates for the virtual illumination position in the sphericalcoordinate system.

The β function of Equation 8, i.e., β(φ,θ), is a value which isdetermined based on the position of virtual illumination. In oneexemplary embodiment, the β function may take the same form as aGaussian function. In particular, the β function used in operation ofthe second conversion function F2 may be expressible by Equation 5described above. In addition, as described above, in a case in which φand θ are defined as illustrated in FIG. 5, first, the θ value may beconverted by using Equations 6 and 7. In this case, when the virtualillumination is located at a front side of the object ob, the θ value isconverted by using Equation 6, and, when the virtual illumination islocated at a rear side of the object ob, the θ value is converted byusing Equation 7.

As described above, Equation 8 includes the β function. Thus, as the βvalue which is obtained as a result of calculation by using the βfunction varies, the second conversion function F2 also varies. Asdescribed above, because the β value varies based on the virtualillumination position, the second conversion function F2 as expressed byEquation 8 also varies based on the virtual illumination position.

In Equation 8, α is a constant which is selectable by a user or aconstant that may be preset in the image processing apparatus M or thelike. The form of the second conversion function F2 of Equation 8 mayalso be determined by the constant α.

FIG. 9 is a graph which illustrates forms of the second conversionfunction F2 as expressed by Equation 8 based on a change in the β valuewhich is obtained as a result of calculation by the β function. In FIG.9, x axis denotes a respective image value (i.e., x in Equation 8) ofeach voxel or pixel of the projection image which is input to the imagecorrection unit 140. In particular, the x-axis denotes image inputvalues. The y-axis denotes result values which correspond to the xvalues obtained as a result of calculation by Equation 8. In particular,the y axis denotes a respective image output value of each voxel orpixel of the result image after correction.

As illustrated in FIG. 9, the second conversion function F2 has aconcave shape. In this case, the form of the second conversion functionF2 is determined based on the β value which is obtained as a result ofcalculation by using the β function.

As illustrated in FIG. 9, when the β value is small, e.g., beta=0.1, aplot for the second conversion function F2 is represented as a nearlylinear-shaped smooth curve. In this aspect, in all of the ranges of theplot, as the image input value increases, the image output valueincreases approximately proportionally to the image input value. Thus, arespective image output value of each pixel or voxel that isapproximately proportional or proportional to a corresponding imageinput value of each pixel or voxel is obtained.

As the β value increases, a curvature of the plot for the secondconversion function F2 increases, as illustrated in FIG. 9. The plotshave a shape which protrudes leftward and upward. In this case, when theimage input values are small, e.g., in a range of between 0 and 50, theimage output values are rapidly changed, even with respect to arelatively small change of the image input values. As the image inputvalues increase to above a particular value, a respective change in theimage output values based on a corresponding change in the image inputvalues becomes slow, and, when the image input values are certainvalues, e.g., 120 or greater, the image output values are the same orapproximate to each other in spite of the corresponding change in theimage input values.

In particular, as the image input value increases, a tangent slope ateach point of the second conversion function F2 gradually decreases. Inthis case, as illustrated in FIG. 9, as the β value of the secondconversion function F2 increases, the tangent slope at each point of thesecond conversion function F2 rapidly decreases in correspondence withan increase of the image input value. Conversely, when the β value ofthe second conversion function F2 is small, the tangent slope smoothlydecreases.

When the β value of the second conversion function F2 is very high,e.g., beta=1, the curvature of the plot of the second conversionfunction F2 is relatively large. As illustrated in FIG. 9, even when theimage input value is small, a very high image output value may beobtained. In addition, when respective image input values of a pluralityof pixels or voxels are small, e.g., 85 or less, a difference betweencorresponding image output values of the pixels or voxels is relativelylarge, even though a difference between the image input values of thepixels or voxels is relatively small.

As described above, the β value varies based on coordinates of thevirtual illumination position, and the form of the second conversionfunction F2 varies based on a change in the β value, as illustrated inFIG. 9. Thus, by applying the second conversion function F2 to imagedata, voxel or pixel values of each image may be corrected differentlyfrom each other based on a virtual illumination position which isselected by a user or preset in the image processing apparatus M, and animage contrast may also be adjusted based on the virtual illuminationposition.

The third correction unit 143 of the image correction unit 140 may beconfigured to adjust a color (i.e., a color value) of the projectionimage which is acquired by the projection image acquisition unit 120. Inone exemplary embodiment, the third correction unit 143 may adjust thecolor of the projection image by using the third conversion function F3which is acquired by reading the conversion function database 150. Insome exemplary embodiments, the third correction unit 143 may not onlyadjust the color value but also correct a luminance of the image. Inparticular, the third correction unit 143, in addition to the firstcorrection unit 141, also corrects the luminance of the acquired image.

In particular, in one exemplary embodiment, the third conversionfunction F3 may be expressible by Equation 9 below:C(x,s,φ,θ)=x·s·[1−ϵ)+ϵ·l(φ,θ)]  [Equation 9]

In Equation 9, x denotes a respective image value of an object which isinput to each voxel of image data. In particular, as described above, xis a respective image value of each voxel collected by the image datacollector 10. In addition, φ and θ denote coordinates which arecalculated by the coordinate converter 132 or the like or pre-givencoordinates for the virtual illumination position in the sphericalcoordinate system.

In addition, s denotes a value of a shadow that is applied or to beapplied to an image, ϵ denotes a separately determined luminanceattenuation constant, and l(φ,θ) denotes a luminance attenuation valuewhich is determined based on the virtual illumination position. In someexemplary embodiments, l(φ,θ) as used by the third correction unit 143may be the same as that used by the first correction unit 141. Inparticular, the l(φ,θ) of Equation 9 may be determined by applying thesame numerical expression as that of Equation 4.

Referring to Equation 9, the corrected image value of each voxel of theprojection image according to Equation 9 may be determined by an imagevalue of each voxel subjected to rendering by the rendering unit 110, aseparately added shadow value for each voxel, and a luminanceattenuation value based on the virtual illumination position. In thiscase, the luminance attenuation value based on the virtual illuminationposition may be selectable by a user, or a weight may be applied theretoby a luminance attenuation constant that is preset and pre-stored in theimage processing apparatus M.

The hue of an image may be varied based on Equation 9 described above.In addition, a luminance value of the image may also be similarlychanged.

As described above, the image correction unit 140 may perform imagecorrection with respect to the acquired projection image by using thefirst, second, and third correction units 141, 142, and 143 sequentiallyaccording to a predetermined order, e.g., in the order of the first,second and third correction units 141, 142 and 143, or in a randomorder. In addition, the first, second and third correction units 141,142 and 143 may all serve to correct the projection image, or any one ortwo of the first, second and third correction units 141, 142 and 143 maybe configured to correct the projection image. The image correctionorder of the first, second, and third correction units 141, 142, and 143or selection of at least one of the first, second and third correctionunits 141, 142 and 143 may be determined by a user or based on settingsthat are pre-stored in the image processing apparatus M.

The result images which have been corrected by the image correction unit140 are output to the outside via the output unit 102 which is installedin the image processing apparatus M, or via any one or more of variousimage display devices which are provided with a display module which isconnected to the image processing apparatus M via a wired or wirelesscommunication network, e.g., a computer monitor, a notebook, a tabletPC, a smart phone, and the like. Accordingly, a user can view thecorrected image of the object ob.

FIGS. 10A and 10B illustrate images which are acquired by correctingimages of the object ob which are obtained when the virtual illuminationis emitted respectively toward the rear and front surfaces of the objectob.

In particular, FIG. 10A illustrates an image which has been corrected bythe second correction unit 142 of the image correction unit 140 in acase in which a direction of the view point is on the front side of theobject ob and the virtual illumination is emitted toward the rearsurface of the object ob. In this regard, the corrected image isacquired such that the second correction unit 142 performs a tonemapping with respect to the acquired projection image by using thesecond conversion function F2 which is expressible by Equation 9. Theimage shown in FIG. 10A has a relatively higher contrast than the imageof FIG. 4A, and thus, the object ob, e.g., each part of the face of thefetus (e.g., eyes, nose, mouth and the like) may be more clearlyrecognized.

FIG. 10B is an image which has been corrected by the first and secondcorrection units 141 and 142 of the image correction unit 140 in a casein which both of the view point and the virtual illumination unit arepositioned on the front side of the object ob. In this regard, thecorrected image is acquired by applying the first conversion function F1which is expressible by Equation 4 and the second conversion function F2which is expressible by Equation 8 to the acquired projection image. Theimage of FIG. 10B has a more attenuated luminance and a relativelyhigher contrast than those of the image of FIG. 4B, as a result ofapplication of the first and second conversion functions F1 and F2.Thus, it can be seen that it is relatively easy to recognize the objectob, e.g., each part of the face of the fetus and the corrected image hasimproved 3D properties.

FIG. 11 is a perspective view of an ultrasonic imaging apparatus,according to an exemplary embodiment. FIG. 12 is a block diagram whichillustrates a configuration of the ultrasonic imaging apparatus,according to an exemplary embodiment.

The ultrasonic imaging apparatus is an imaging apparatus that transmitsultrasonic waves to an object ob, e.g., a target site inside the objectob through the surface of a human body, collects ultrasonic waves whichare reflected from the target site, and generates a sectional image ofvarious tissues or structures inside the object ob by using thecollected ultrasonic waves. In particular, as illustrated in FIGS. 11and 12, the ultrasonic imaging apparatus may include an ultrasonic probeP and a main body M.

As illustrated in FIG. 12, the ultrasonic probe P is provided at an endportion of the main body M with a plurality of ultrasound transducers P1which are configured to generate ultrasonic waves by using alternatingcurrent which is supplied from a power source P2, direct the generatedultrasonic waves toward the object ob, receive an ultrasound echo signalwhich is reflected from a target site inside the object ob, and convertthe received ultrasound echo signal into an electrical signal. In thisregard, the power source P2 may include at least one of an externalpower source, a storage battery installed in the ultrasonic imagingapparatus, and/or the like. Examples of the ultrasound transducers P1include a magnetostrictive ultrasonic transducer which uses amagnetostrictive effect of a magnetic body, a piezoelectric ultrasonictransducer which uses a piezoelectric effect of a piezoelectricmaterial, and a capacitive micromachined ultrasonic transducer (cMUT),which transmits and receives ultrasonic waves by using vibrations ofseveral hundreds or several thousands of micromachined thin films.

When alternating current is supplied to the ultrasound transducers P1from the power source P2, piezoelectric vibrators or thin films of theultrasound transducers P1 vibrate and, as a result, ultrasonic waves aregenerated. The generated ultrasonic waves are directed toward the objectob, e.g., into the human body. The directed ultrasonic waves arereflected by at least one target site which is located at any one ormore of various depths from within the object ob. The ultrasoundtransducers P1 receive ultrasound echo signals which are reflected fromthe target site and convert the received ultrasound echo signals into anelectrical signal, thereby obtaining a plurality of received signals.

The received signals are transmitted to the main body M via a wired orwireless communication network. The ultrasonic probe P receives theultrasound echo signal via at least one of a plurality of channels, andthus the received signals are also transmitted to the main body M via atleast one of the channels.

The main body M may include a beamforming unit M01 (also referred toherein as a beamformer M01), a volume data generator M02, a renderingunit M11 (also referred to herein as a renderer M11), a projection imageacquisition unit M12 (also referred to herein as a projection imageacquirer M12), a virtual illumination processor M13, an image correctionunit M14 (also referred to herein as an image corrector M14), and aconversion function database M15. In some exemplary embodiments,however, some of the above-described elements may be omitted from themain body M.

The beamforming unit M01 performs beamforming based on the plurality ofreceived signals. In this regard, beamforming is a process of focusing aplurality of received signals which are input via at least one of aplurality of channels in order to acquire an appropriate ultrasoundimage of the interior of the object ob.

The beamforming unit M01 corrects a time difference in the receivedsignals which is caused by a difference in distances between eachultrasound transducer P1 and the target site inside the object ob. Inaddition, the beamforming unit M01 emphasizes a plurality of receivedsignals of a specific channel and/or relatively attenuates a pluralityof received signals of another channel, thereby focusing the receivedsignals. In this case, the beamforming unit M01 may emphasize andattenuate specific received signals by or without, for example, adding apredetermined weight to the received signals which are input via eachchannel.

In addition, the beamforming unit M01 may focus a plurality of receivedsignals which are collected by the ultrasonic probe P for each of aplurality of frames by considering a position and a focal point of aconversion element of the ultrasonic probe P.

Further, beamforming which is performed by the beamforming unit M01 mayinclude data-independent beamforming and/or adaptive beamforming.

The volume data generator M02 generates ultrasound image data based onthe signals focused by the beamforming unit M01. When the beamformingunit M01 focuses a plurality of received signals for each frame, aplurality of ultrasound image data which respectively correspond to eachframe is generated based on the focused signals. In this regard, thegenerated ultrasound image data may include 3D ultrasound image datawhich relate to the object ob, i.e., volume data which relate to theobject ob.

The rendering unit M11 renders ultrasound image data, e.g., volume datawhich relate to the object ob, in order to reconstruct a 2D or 3D imageof the object ob. When the image data collected by the image datacollector 10 are volume data, the rendering unit M11 performs volumerendering by using the volume data. In addition, the rendering unit M11may reconstruct an image by applying, to the rendering process, a shadowmap which is generated based on the position of virtual illuminationthat is received by the virtual illumination processor M13 or is storedbeforehand. In this regard, the rendering unit M11 may receive a shadowmap from the outside or generate a shadow map based on the position ofvirtual illumination received by the virtual illumination processor M13.The rendering unit M11 may reconstruct a shaded 3D image through suchshadow mapping.

In one exemplary embodiment, the ultrasonic imaging apparatus mayfurther include the projection image acquisition unit M12. Theprojection image acquisition unit M12 may acquire a 2D image of theobject ob which corresponds to at least one view point based on the 3Dimage subjected to volume rendering by the rendering unit M11. In thisregard, the at least one view point may be input via an external inputunit i and may also be determined based on settings stored in theultrasonic imaging apparatus.

In another exemplary embodiment, the projection image acquisition unitM12 may acquire a projection image for the result image which iscorrected by the image correction unit M14, which will be describedbelow.

The virtual illumination processor M13 transmits information whichrelates to a position of virtual illumination to be emitted toward theobject ob, i.e., a virtual illumination position, to the rendering unitM11, the image correction unit M14, or the like. The rendering unit M11,having received the virtual illumination position, performs volumerendering by applying a shade based on the virtual illumination, and theimage correction unit M14 corrects an image of the object ob, e.g., aprojection image, by using the virtual illumination.

According to one or more exemplary embodiments, the virtual illuminationprocessor M13 may determine the position of the virtual illuminationwhich is emitted toward the object ob based on instructions or commandswhich are received via the input unit i from a user. In anotherexemplary embodiment, information which relates to the virtualillumination during shadow mapping performed by the rendering unit M11is received from the rendering unit M11, and the position of the virtualillumination to be used in the image correction unit M14 may bedetermined based on the received information which relates to thevirtual illumination.

In addition, when the determined virtual illumination position isrepresented in a rectangular coordinate system, the virtual illuminationprocessor M13 may transform the coordinates in the rectangularcoordinate system into coordinates in a spherical coordinate system. Inthis case, coordinate conversion of the virtual illumination may beperformed by using Equations 1, 2, and 3 as described above.

The image correction unit M14 corrects the volume data which issubjected to rendering performed by the rendering unit M11 or theprojection image acquired by the projection image acquisition unit M12.In this case, the image correction unit M14 receives the virtualillumination position from the virtual illumination processor M13 andcorrects the image by using the received virtual illumination position.

The image correction unit M14 first receives conversion functions foruse in performing image correction by reading the conversion functiondatabase M15 connected thereto. In this case, the conversion functionsmay include at least one of the first, second and third conversionfunctions F1, F2 and F3.

In order to correct a luminance of the acquired image, for example, theimage correction unit M14 calls the first conversion function F1 whichis expressible by Equation 4 from the conversion function database M15and substitutes the virtual illumination position received from thevirtual illumination processor M13 into the first conversion functionF1, thereby correcting the luminance of the acquired image.

In order to correct a contrast of the acquired image, for example, theimage correction unit M14 calls the second conversion function F2 whichis expressible by Equation 8 and substitutes the virtual illuminationposition into the second conversion function F2, thereby correcting thecontrast of the image.

In order to correct a hue of the acquired image, for example, the imagecorrection unit M14 calls the third conversion function F3 which isexpressible by Equation 9 and substitutes the virtual illuminationposition into the third conversion function F3, thereby correcting thehue of the image.

In this regard, the image correction unit M14 may correct the luminance,the contrast, and the hue of the image at once, or the image correctionunit M14 may correct only any one or two of the luminance, the contrast,and the hue of the image.

In addition, in order to correct the luminance, the contrast, and/or thehue of the image, the image correction unit M14 may first calculate theβ value that is used in Equations 4, 8 and 9. In this regard, the βvalue may be determined by applying a β function which is expressible byEquation 5.

The image correction unit M14 corrects the volume data of the object obor the projection image of the object ob which corresponds to at leastone view point by using the received or read-out virtual illuminationposition and the first, second and third conversion functions F1, F2 andF3, thereby generating a result image. In this regard, the result imagemay include a 2D image. In some exemplary embodiments, predeterminedimage processing may be further performed on the result image in orderto generate a stereoscopic image.

The generated result image is displayed on a display unit d which isinstalled in the ultrasonic imaging apparatus or connected thereto via awired or wireless communication network, e.g., a display module such asa monitor, a tablet PC, a smart phone, or the like. An example of theresult image which may be displayed on the display unit d is illustratedin each of FIG. 10A and FIG. 10B.

Although FIGS. 11 and 12 illustrate that the main body M includes thebeamforming unit M01, the volume data generator M02, the rendering unitM11, the projection image acquisition unit M12, the virtual illuminationprocessor M13, the image correction unit M14, and the conversionfunction database M15, exemplary embodiments are not limited thereto. Inparticular, the main body M need not include all of the above-listedelements. Some of the elements may also be installed in another part ofthe ultrasonic imaging apparatus, e.g., the ultrasonic probe P.

For example, the ultrasonic imaging apparatus may include thebeamforming unit M01, the volume data generator M02, the rendering unitM11, the projection image acquisition unit M12, the virtual illuminationprocessor M13, the image correction unit M14, and the conversionfunction database M15, so that the ultrasonic probe P is configured togenerate an ultrasound image based on an electrical signal by apredetermined process and to correct the generated ultrasound image. Inaddition, an information processor which is connected to the main body Mor the like may include some of the above-listed elements, e.g., theconversion function database M15, and the main body M may include thebeamforming unit M01, the volume data generator M02, the rendering unitM11, the projection image acquisition unit M12, the virtual illuminationprocessor M13, and the image correction unit M14.

FIG. 13 is a flowchart which illustrates an image processing method,according to an exemplary embodiment.

As illustrated in FIG. 13, in the image processing method according toan exemplary embodiment using virtual illumination, first, in operationS200, the image processing apparatus performs rendering of collectedimage data which relates to an object ob in order to reconstruct a 2D or3D image of the object ob. In this case, when the collected image dataare volume data, volume rendering is performed. In some exemplaryembodiments, volume rendering may be performed by applying a shadow mapfor a shadow at a predetermined virtual illumination position withrespect to the image data, i.e., shadow mapping.

In this regard, the virtual illumination position of the object ob isdetermined by external input or based on settings that are preset in theimage processing apparatus. When shadow mapping is performed, inoperation S210, the virtual illumination position of the object ob maybe determined based on the position of virtual illumination used duringshadow mapping. When the virtual illumination position is represented bycoordinates in a rectangular coordinate system, the coordinates in therectangular coordinate system may be converted into coordinates in aspherical coordinate system, thereby obtaining a virtual illuminationposition which is represented by coordinates in the spherical coordinatesystem.

In addition, at least one conversion function is simultaneously input orcalled. In this regard, the input or called conversion function may beexpressible by at least one of Equation 4, Equation 8, and Equation 9.In this regard, each of Equation 4, Equation 8, and Equation 9 includesthe β value which is expressible by Equation 5, and the β value variesbased on the virtual illumination position, and thus, the at least oneconversion function varies based on the virtual illumination position.

In operation S220, the determined virtual illumination position issubstituted into the input or called conversion function and then therendered image is corrected by using the at least one conversionfunction.

As a result, the resulting corrected image is acquired in operationS230. In this regard, when the corrected image includes a 3D image, theacquired image may include a 2D projection image which is generated forthe corrected image. In addition, in at least one exemplary embodiment,predetermined image processing may be further performed on the correctedrendered image in order to generate a stereoscopic image as the resultimage.

FIG. 14 is a flowchart which illustrates an image processing method,according to another exemplary embodiment.

As illustrated in FIG. 14, in operation S300, volume rendering isperformed upon the collected volume data which relates to an object obin order to obtain 3D image data. Subsequently, in operation S310, aprojection image which corresponds to at least one view point may beacquired by calculation which is based on the 3D image data which hasbeen subjected to the volume rendering process. Even in the presentexemplary embodiment, the volume rendering process may be performed inconjunction with the shadow mapping process, similarly as has beendescribed above.

Next, in operation S320, a virtual illumination position of the objectob is determined. In this case, the virtual illumination position may beinput from the outside. When shadow mapping is performed upon the volumedata, in operation S320, the virtual illumination position of the objectob may be determined based on the position of virtual illumination usedduring the shadow mapping process. When the virtual illuminationposition is represented by coordinates in a rectangular coordinatesystem, the coordinates in the rectangular coordinate system may beconverted into coordinates in a spherical coordinate system.

In operation S330, at least one of the first, second and thirdconversion functions F1, F2 and F3 is called as desired. In this regard,the first conversion function F1 may be called in order to correct aluminance of the acquired image, and the second conversion function F2may be called in order to correct a contrast of the acquired image. Inaddition, the third conversion function F3 may be called in order tocorrect a hue of the acquired image. In this regard, the firstconversion function F1 may be expressible by Equation 4, the secondconversion function F2 may be expressible by Equation 8, and the thirdconversion function F3 may be expressible by Equation 9.

In operation S340, the determined virtual illumination position issubstituted into the at least one of the first, second and thirdconversion functions F1, F2 and F3 and the received projection image iscorrected by using the conversion functions based on the virtualillumination position.

As a result, in operation S350, the result image is acquired and theacquired image is displayed to a user via a display device.

FIG. 15 is a flowchart which illustrates a process for correcting animage based on a virtual illumination position.

In one exemplary embodiment, when a determination is made in operationS400 that the virtual illumination position that is input by a user ordetermined based on settings that are preset in the image processingapparatus is the same or approximately the same as a direction of theview point, i.e., when the virtual illumination unit is positioned at aposition a3 (see FIG. 3) such that the virtual illumination is directedtoward the front of the object, first, in operation S410, the θ valuemay be converted according to Equation 6 in order to obtain a θ′ valuefor the application of the first, second and third conversion functionsF1, F2 and F3.

Then, in operation S411, the β value is calculated based on thegenerated virtual illumination position (θ′, φ). In one exemplaryembodiment, the β value may be expressible by Equation 5 as describedabove.

For example, in operation S412, the first conversion function F1 whichis expressible by Equation 4 is called, and the image is corrected byusing the first conversion function F1. In this regard, the firstconversion function F1 includes the β value as described above and the βvalue varies based on the virtual illumination position, and thus, thefirst conversion function F1 also varies based on the virtualillumination position. As a result of this correction, the luminance ofthe image is corrected.

Subsequently, for example, in operation S413, the second conversionfunction F2 which is expressible by Equation 8 is called, and then theimage is corrected by using the second conversion function F2.Similarly, the second conversion function F2 also includes the β valueand thus varies based on the virtual illumination position. As a resultof this correction, the contrast of the image is corrected.

In another exemplary embodiment, when a determination is made inoperation S400 that the virtual illumination position that is input by auser or determined based on settings that are preset in the imageprocessing apparatus is approximately opposite to a direction of theview point with respect to the object ob, i.e., when the virtualillumination unit is positioned at a position a1 (see FIG. 3) such thatthe virtual illumination is directed from a back side with respect tothe object, first, in operation S420, the θ value may be convertedaccording to Equation 7 in order to obtain a θ′ value for application ofthe first, second and third conversion functions F1, F2 and F3.

Subsequently, in operation S421, the β value is calculated based on thegenerated virtual illumination position. The β value may be expressibleby Equation 5 as described above.

When the virtual illumination is positioned in a direction which isapproximately opposite to that of the view point with respect to theobject, only the second conversion function F2 may be called, asillustrated in FIG. 15, in order to enhance image contrast. Then, inoperation S422, the image processing apparatus corrects the image byusing the called second conversion function F2.

In operation S430, the corrected result image is externally displayed ona display device or the like. Thus, a user can view the image with aluminance, contrast, and/or hue value that is corrected based on thevirtual illumination position.

As is apparent from the above description, according to the imageprocessing apparatus and method, an image of an object may be naturallydisplayed based on a change in the position of virtual illumination, andan image with improved quality may be acquired.

In addition, in image processing of an image which is subjected tovolume rendering, 3D properties, luminance, hue, and/or contrast of animage may be improved by applying at least one conversion function thatvaries based on the position of virtual illumination, whereby the imagemay be more realistically displayed.

Moreover, when the virtual illumination unit is located at a rear sideof the object, an image of the object which has a semi-transparenteffect may be generated. When the virtual illumination is emitted towardthe object from a front side of the object, an image which has highcontrast may be generated. Therefore, an image which has excellentreadability may be provided to a user.

Although a few exemplary embodiments have been shown and described, itwill be appreciated by those skilled in the art that changes may be madein these exemplary embodiments without departing from the principles andspirit of the present inventive concept, the scope of which is definedin the claims and their equivalents.

What is claimed is:
 1. An image processing method comprising:performing, by an image processing apparatus, volume rendering of volumedata which relate to an object and acquiring volume-rendered image data;acquiring information which relates to a virtual illumination position;determining at least one conversion function from a plurality ofconversion functions stored in a database, based on the virtualillumination position which relates to the object; and correcting theacquired image data by using the virtual illumination position and theat least one conversion function, wherein the correcting comprisesperforming a tone mapping with respect to the acquired image data byusing a second conversion function using a difference betweencoordinates of the virtual illumination position and coordinates of areference position, and a distribution of the virtual illuminationposition.
 2. The image processing method according to claim 1, whereinthe correcting further comprises adjusting a brightness of the acquiredimage data by using a first conversion function which is determinedbased on the coordinates of the virtual illumination position.
 3. Theimage processing method according to claim 2, wherein the firstconversion function includes an illumination attenuation function. 4.The image processing method according to claim 2, wherein the firstconversion function includes a function which is expressible by Equation1 below: $\begin{matrix}{{l\left( {\phi,\theta} \right)} = {1 - {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ wherein (φ,θ) denotes respective coordinates of thevirtual illumination position in a spherical coordinate system, (φ₀,θ₀)denotes respective coordinates of a reference position in the sphericalcoordinate system, σ_(φ) and σ_(θ) denote respective values which relateto a distribution of a first virtual illumination position, and Adenotes a predetermined constant.
 5. The image processing methodaccording to claim 1, wherein the second conversion function includes afunction which is expressible by Equation 2 below: $\begin{matrix}{{p\left( {x,\phi,\theta} \right)} = \frac{1}{1 + {\alpha \cdot e^{{- {\beta{({\phi,\theta})}}} \cdot x}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$ wherein x denotes an image value of a respective voxel, φand θ denote respective coordinates of the virtual illumination positionin a spherical coordinate system, a denotes a predetermined constant,and β(φ,θ) denotes a value which is determined based on the virtualillumination position.
 6. The image processing method according to claim5, wherein the β(φ,θ) is determined by applying Equation 3 below:$\begin{matrix}{{\beta\left( {\phi,\theta} \right)} = {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$ wherein (φ₀,θ₀) denotes respective coordinates of areference position in the spherical coordinate system, σ_(φ) and σ_(θ)denote respective values which relate to a distribution of a firstvirtual illumination position, and A denotes a predetermined constant.7. The image processing method according to claim 1, wherein thecorrecting further comprises performing a hue correction with respect tothe acquired image data by using a third conversion function which isdetermined based on the coordinates of the virtual illuminationposition.
 8. The image processing method according to claim 7, whereinthe third conversion function includes a function which is expressibleby Equation 4 below:C(x,s,φ,θ)=x·s·[(1−ϵ)+ϵ·l(φ,θ)]  [Equation 4] wherein x denotes an imagevalue of a respective voxel, s denotes a shadow value, φ and θ denoterespective coordinates of the virtual illumination position in aspherical coordinate system, ϵ denotes a luminance attenuation constant,and l(φ,θ) denotes a luminance attenuation value which relates to thevirtual illumination position.
 9. The image processing method accordingto claim 8, wherein the luminance attenuation value l(φ,θ) is determinedby applying Equation 1 below: $\begin{matrix}{{l\left( {\phi,\theta} \right)} = {1 - {A\; e^{- {({\frac{{({\phi - \phi_{0}})}^{2}}{2\;\sigma_{\phi}^{2}} + \frac{{({\theta - \theta_{0}})}^{2}}{2\;\sigma_{\theta}^{2}}})}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ wherein (φ,θ) denotes respective coordinates of thevirtual illumination position in a spherical coordinate system, (φ₀,θ₀)denotes respective coordinates of a reference position in the sphericalcoordinate system, σ_(φ) and σ_(θ) denote respective values which relateto a distribution of a first virtual illumination position, and Adenotes a predetermined constant.
 10. The image processing methodaccording to claim 1, wherein the correcting further comprises, when thevirtual illumination position is represented by coordinates in arectangular coordinate system, converting the coordinates whichrepresent the virtual illumination position from the rectangularcoordinate system into coordinates in a spherical coordinate system. 11.The image processing method according to claim 1, wherein the acquiringcomprises acquiring shaded volume-rendered image data which relate tothe object via volume rendering which is performed by using a shadow mapin conjunction with virtual illumination.
 12. An image processingapparatus comprising: a volume data collector which is configured tocollect volume data which relate to an object; and an image processorconfigured to perform volume rendering of the collected volume datawhich relate to the object and to acquire rendered image data, whereinthe image processor is further configured to acquire information whichrelates to a virtual illumination position, to determine at least oneconversion function from a plurality of conversion functions stored in adatabase based on the virtual illumination position which relates to theobject, and to correct the acquired image data by using the virtualillumination position and the at least one conversion function, andwherein the image processor is further configured to perform a tonemapping with respect to the acquired image data by using a secondconversion function using a difference between coordinates of thevirtual illumination position and coordinates of a reference position,and a distribution of the virtual illumination position.
 13. The imageprocessing apparatus according to claim 12, wherein the image processoris further configured to adjust a brightness of the acquired image databy using a first conversion function which is determined based oncoordinates of the virtual illumination position.
 14. The imageprocessing apparatus according to claim 13, wherein the first conversionfunction includes an illumination attenuation function.
 15. The imageprocessing apparatus according to claim 13, wherein the image processoris further configured to perform a hue correction with respect to theacquired image data by using a third conversion function.
 16. The imageprocessing apparatus according to claim 13, wherein, when the virtualillumination position is represented by coordinates in a rectangularcoordinate system, the image processor is further configured to convertthe coordinates which represent the virtual illumination position fromthe rectangular coordinate system into coordinates in a sphericalcoordinate system.
 17. The image processing apparatus according to claim13, wherein the image processor is further configured to acquirevolume-rendered image data which relate to the object by using a shadowmap in conjunction with virtual illumination.
 18. The image processingapparatus according to claim 13, wherein the image processor is furtherconfigured to acquire a projection image of the object which correspondsto at least one view point with respect to the acquired image data, andto correct the acquired projection image of the object based on thevirtual illumination position by using the at least one conversionfunction.